Strong visible photoluminescence emission of ZnO nanosheets and nanoflowers by a facile hydrothermal route.

Zinc oxide nanostructures such as nanosheets (NS) and nanoflowers (NF) were obtained by a facile hydrothermal synthesis using zinc chloride (ZnCl2) as precursor with low molar concentrations and a short synthesis time (2 h) at 200 °C. By means of X-ray diffraction and Raman spectroscopy measurements, the wurtzite-type ZnO structure was confirmed with high crystalline quality. SEM micrographs showed the influence of ZnCl2 concentration on ZnO morphology; ZnO NF were obtained at low concentrations (0.02 and 0.05 M), while ZnO NS were seen for higher concentrations (0.2-0.6 M) and their thicknesses can be estimated from 15 to 60 nm. In addition, TEM images showed a large number of pores with sizes below 15 nm in both ZnO nanostructures. Raman and photoluminescence displayed the surface defects density for ZnO nanostructures. Raman spectra showed the E1(LO) mode localized at ∼581 cm-1, associated with oxygen vacancies and zinc interstitials, being more intense for ZnO NF, while photoluminescence results showed a strong yellow-orange emission (centered from 587 to 618 nm) relative to UV emission, being more intense for ZnO NF. These properties reveal further potential for high performance luminescent devices based on ZnO NF and NS.

Polymorphous silicon thin films obtained by plasma-enhanced chemical vapor deposition using dichlorosilane as silicon precursor.

Polymorphous silicon thin films (pm-Si) have been deposited from mixtures of dichlorosilane and hydrogen, using argon as the diluting gas by plasma-enhanced chemical vapor deposition. The deposition conditions were chosen to simultaneously obtain both Si nanocrystallites and an amorphous silicon matrix in the as-grown samples. High resolution transmission electron microscopy studies show the crystallinity of Si domains whose dimensions are in the interval of 2-14 nm. The surface passivation state of the silicon nanocrystals was inferred from Fourier transform infrared spectroscopy analysis. Two optical absorption edges, corresponding to the amorphous matrix and the Si nanocrystals, were observed for all the pm-Si thin films. Intense visible photoluminescence was observed for the as-grown samples. The possibility of using these thin films for the down-conversion effect in silicon solar cells is discussed.